This invention relates to a hoist control valve interlock system for use in trolley-assisted dump trucks.
In view of the availability of petroleum becoming tight increasingly in the recent years, there is a relevant tendency towards energy saving even in large mines. In particular, in the districts where sufficient power can be generated by hydraulic power and by thermal power obtained by farming coals, but are lacking in petroleum resources, there can be seen a strong demand for replacing petroleum driven mining machines by electrically driven mining machines in order to save petroleum products.
Besides the tendency of petroleum saving, there can be seen a tendency of falling productivity due to the suspension of movements of vehicles so as to prevent a pit of the mine from oxygen deficient condition arising from the exhaust gas smog emitted from the engines of ore carrying vehicles and the amount of which increases as the pit becomes deeper.
In order to eliminate such troubles in the late years, there has been proposed a double-wire trolley assisted dump truck system utilizing a cheap commercial power supply on the ascent courses extending from the bottom of the pits to the dumping areas. If the operator of the trolley-assisted dump truck manipulates by mistake the hoist control lever for controlling the dump vessel during running on an ascent course under the trolley mode condition, then the hoist valve is rendered operative to allow upward movement of the dump vessel, so that the trolley wires through which electric current flows are cut off by the lifted dump vessel thereby causing a big accident.